Exactly what the title says, Christianity in all its various strains still stems from the horrendous old testament, and with all the awful shit that endorses, as well as with things like Calvinism and the general doomsday cult foundations in the religion, why do some people still act so charitably towards it? Christianity has proven itself to be a morally corrupt and oppressive institution at every turn. Or maybe I'm just too negative? 
EDIT Ok guys I get it this was rather reductionist, and I definitely was disregarding all the good that religious folks have done, and that religion has inspired people to do, but again over correcting into enthusiastic support for religion can also be problematic.
I haven't really honed this line of thought, but something I've thought about recently is how churches could be, for lack of a better word, co-opted here in the US to fight for left-wing causes. There's a church out in San Francisco called GLIDE that was a part of the Methodist Church (I think they broke off) that essentially operates as a neighborhood resource center. Daily soup kitchen (3 meals every single day, no limits), harm-reduction kit distribution, childcare, DV resource center, and a lot more.
I guess all I've been thinking is just that if more churches could be politicized in this way, they could be potential allies in local struggles, because they're already organized, meet regularly, have physical spaces that can be used, and know how to handle a budget.